Sending email from web interface works, sending from Thunderbird via SMTP shows duplicate email

Sending email from web interface works, sending from Thunderbird via SMTP shows duplicate email

I made some sending tests today via browser and via Thunderbird client to a temporary guerrilla email address,
I discovered that sending email from the zoho web interface works, while sending from Thunderbird via SMTP shows duplicate email in the sent box but no email is received at the other end.

The same Thunderbird configuration worked up until today!